Manufacturing Nanoparticles with Orthogonally Adjustable Dispersibility in Hydrocarbons, Fluorocarbons, and Water

Article abstract of DOI:10.1002/open.201800011

We describe a universal wet-chemical shell-by-shell coating procedure resulting in colloidal titanium dioxide (TiO₂) and iron oxide (Fe₃O₄) nanoparticles with dynamically and reversibly tunable surface energies. A strong c

Full text of DOI:10.1002/open.201800011

DOI: 10.1002/open.201800011
Manufacturing Nanoparticles with Orthogonally
Adjustable Dispersibility in Hydrocarbons, Fluorocarbons,
and Water
Lukas Zeininger,[a] Lisa M. S. Stiegler,[a] Luis Portilla,[b] Marcus Halik,[b] and Andreas Hirsch*[a]
We describe a universal wet-chemical shell-by-shell coating
procedure resulting in colloidal titanium dioxide (TiO2) and iron
oxide (Fe3O4) nanoparticles with dynamically and reversibly
tunable surface energies. A strong covalent surface functionali-
zation is accomplished by using long-chained alkyl-, triethylen-
glycol-, and perfluoroalkylphosphonic acids, yielding highly sta-
bilized core–shell nanoparticles with hydrophobic, hydrophilic,
or superhydrophobic/fluorophilic surface characteristics. This
covalent functionalization sequence is extended towards a
second noncovalent attachment of tailor-made nonionic am-
phiphilic molecules to the pristine coated core–shell nanoparti-
cles via solvophobic (i.e. either hydrophobic, lipophobic, or flu-
orophobic) interactions. Thereby, orthogonal tuning of the sur-
face energies of nanoparticles via noncovalent interactions is
accomplished. As a result, this versatile bilayer coating process
enables reversible control over the colloidal stability of the
metal oxide nanoparticles in fluorocarbons, hydrocarbons, and
water.
1. Introduction
Metal oxide nanoparticles exhibit unique size-related proper-
ties and have been implemented as central components of a
large variety of electronic,[1,2] catalytic,[3] medical,[4,5] and per-
formance materials.[6] With regard to their use in technological
applications, major focus in nanoparticle research is directed
towards 1) a generation of colloidal stability of the nanoparti-
cles in solutions,[7] 2) directing their self-assembly into nano-
structures,[8–10] and 3) controlling their wettability characteris-
tics.[11,12] By using a chemical surface modification with organic
molecular self-assembled monolayers (SAMs), the chemical and
physical surface properties of thermodynamically unstable
nano-sized particles can be controlled.[13] At the same time,
most of the inherent material properties can be maintained.
This is why most procedures for the synthesis of nanoparticles
provide an in situ capping agent to sterically and/or electro-
statically stabilize the newly formed nanocrystals.[14,15] However,
a substitution of this stabilizing ligand shell in order to cus-
tomize the surface properties of nanoparticles can be problem-
atic as this can promote irreversible changes to the nanoparti-
cles, including Ostwald ripening, which can ultimately lead to
unwanted agglomeration and growth, causing a loss of the
nanoparticles’ special properties.[16] Approaches to circumvent
these complications rely on a property management of the ini-
tial ligand capped nanoparticles. By modification of the exist-
ing ligand shell, the polarity of the nanoparticle surfaces can
be reversed and colloidal stability in aqueous environments
can be generated. Examples include a chemical modification of
the ligand on the surface by chemical reactions (e.g. oxida-
tions) or the establishment of an additional thin layer of inor-
ganic or organic building blocks (e.g. with amphiphilic co-poly-
mers).[17,18] However, despite its relevance, there is no general-
izable route towards a switchable reversion of polarity of SAM-
stabilized nanoparticles in various orthogonal solvents such as
water, polar and apolar hydrocarbons, or superhydrophobic
environments such as fluorocarbons. As such, a noncovalent
self-assembly of small functional nonionic amphiphiles with
pristine coated nanoparticles represents a very gentle and
straightforward approach. This includes the introduction of
new nanoparticle coating concepts, for example, employing
amphiphilic fluorocarbons. At the same time, the scope of
processability and practical application could be considerably
broadened towards new options for the preparation of nano-
particle thin films as well as for the selective scavenging of am-
phiphilic components by core–shell colloids.
[a] Dr. L. Zeininger, L. M. S. Stiegler, Prof. Dr. A. Hirsch
Department of Chemistry & Pharmacy
Friedrich Alexander University (FAU)
Henkestrasse 42, 91054 Erlangen (Germany)
E-mail: andreas.hirsch@fau.de
[b] Dr. L. Portilla, Prof. Dr. M. Halik
Department of Materials Science
Friedrich Alexander University (FAU)
Martensstrasse 9, 91058 Erlangen (Germany)
Supporting Information and the ORCID identification number(s) for the
author(s) of this article can be found under https://doi.org/10.1002/
open.201800011.
In this work, we introduce for the first time an entirely or-
thogonal tool kit for switchable nanoparticle functionalization.
This concept relies on a combination of a strong covalent sur-
face functionalization with noncovalent bilayer coating, using a
set of amphiphiles with a permutation of terminal polarity,
namely hydrophilic, lipophilic, and fluorophilic (Scheme 1). In a
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This is an open access article under the terms of the Creative Commons
Attribution-NonCommercial-NoDerivs License, which permits use and
distribution in any medium, provided the original work is properly cited,
the use is non-commercial and no modifications or adaptations are
made.
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Scheme 1. Conceptional sketch of our orthogonal bilayer coating strategy. A combination of a strong covalent surface passivation of metal oxide nanoparti-
cles with phosphonic acids 1, 2, and 3 and a subsequent noncovalent solvophobic interaction driven bilayer formation with amphiphiles 4, 5, and 6 leads to
nanoparticles, which can reversibly adjust their surface energies resulting in colloidal stability in hydrocarbons, fluorocarbons and water.
first step, metal oxide nanoparticles (MOx; namely titanium di-
oxide or iron oxide) were covalently functionalized in a wet-
chemical functionalization approach with three different phos-
phonic acid derivatives, namely hexadecylphosphonic acid
(HC-PA 1), (2-(2-(2-hydroxyethoxy)ethoxy)ethyl)phosphonic acid
(PEG-PA 2), and (3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadeca-
fluorodecyl)phosphonic acid (FC-PA 3). Through this stable sur-
face passivation, colloidal stability of the coated nanoparticles
[MOx-PA-HC], [MOx-PA-PEG], and [MOx-PA-FC] was achieved in
hydrocarbons, water, and fluorocarbons, respectively. To rever-
sibly tune the surface properties of these lipophilic, hydrophil-
ic, and fluorophilic particles, and thus their dispersion behavior,
we added new tailor-made nonionic amphiphilic molecules
HC-PEG 4, FC-PEG 5, and HC-FC 6. The key was a noncovalent
solvophobic interaction-driven self-assembly of these amphi-
philic molecules 4–6 with the shells of stable phosphonic-acid-
functionalized nanoparticles [MOx-1], [MOx-2], and [MOx-3]. As
a result, this shell-by-shell coating approach allowed for the
manufacturing of nanoparticles with orthogonally adjustable
and switchable colloidal stability in hydrocarbons, fluorocar-
bons, and water.
TiO2 nanoparticles and superparamagnetic Fe3O4 nanoparticles.
The average diameter sizes were 34 and 15 nm, respectively.
As for the wet-chemical surface functionalization, we sonicated
0.15 wt% suspensions of metal oxide nanoparticles in a
5.0 mm solution of HC-PA 1, PEG-PA 2, and FC-PA 3 in isopro-
panol, followed by centrifugation of the functionalized material
in order to separate from non-surface-adsorbed organic mole-
cules. The functionalized material was characterized by using
thermogravimetric analysis (TGA), Fourier-transform infrared
spectroscopy (FTIR), static contact angle (SCA), as well as dy-
namic light scattering (DLS) measurements (see the Supporting
Information). Althoguh metal oxide nanoparticles functional-
ized with a monolayer of PEG-PA 2 were highly hydrophilic
and, thus, dispersible in aqueous solutions, [MOx-1] and [MOx-
3] readily sediment from polar solutions. The steric stabilization
in [MOx-1] provided lipophilic surface characteristics, rendering
them well dispersible in apolar organic solvents such as tolu-
ene. Fluorinated metal oxide nanoparticles [MOx-3] were non-
dispersible in both, water and toluene, but selectively dis-
solved in fluorocarbon solvents such as perfluoro(methylcyclo-
hexane) (Figure 1).
Surfactant stabilization is a powerful technique for mixing
and dispersing immiscible hydrophobic nanoparticles within a
continuous aqueous phase.[22–24] As we demonstrated in a pre-
vious publication,[25] dispersions of nanoparticles coated with
an alkyl-SAM can be functionalized with ionic as well as zwit-
terionic surfactants in water. To study this hydrophobic interac-
tion driven self-assembly with nonionic surfactants, we synthe-
sized a simple model amphiphile HC-PEG 4 to investigate its
2. Results and Discussion
A covalent surface modification of metal oxide nanoparticles
with phosphonic acid derivatives has been proven to provide
densely packed self-assembled monolayers on the nanoparticle
surface displaying remarkable chemical stability.[19–21] As metal
oxides, we used the commercially available starting materials
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ed undecanoic acid chloride 9 with triethylene glycol afforded
6 in 85% yield.
Upon addition of 4 to hexadecylphosphonic acid functional-
ized nanoparticles [TiO2-1] in water, an immediate increase of
the colloidal stability was noticeable. This stabilizing effect can
be attributed to a hydrophobic interaction driven self-assembly
of the hydrophobic tails of amphiphiles 4 with the hydropho-
bic ligand shell of the functionalized nanoparticle surfaces
[TiO2-1]. The particles act as nucleation sites for a formation of
an orthogonal molecular bilayer around the nanoparticles. In
such a micellar arrangement of the amphiphiles around the
particle cores, the glycol moieties are pointing outwards, pro-
viding colloidal stability in polar solvents such as water. The
extent of the electrosteric stabilization upon addition of am-
phiphiles 4 was characterized by using concentration-depen-
dent zeta-potential measurements (Figure 3a). The zeta poten-
Figure 1. Dispersibility behavior of TiO2 (a) and Fe3O4 (b) nanoparticle mono-
layers coated with HC-PA 1, PEG-PA 2, or FC-PA 3 when dispersed in a three-
phase solvent system of toluene (C7H8), water (H2O), and perfluoro(methylcy-
clohexane) (C7F13).
ability to increase the dispersibility of metal oxide nanoparti-
cles coated with alkyl-phosphonic acid [MOx-1]. The amphi-
phile HC-PEG 4 used in this study was synthesized through the
esterification of lauric acid chloride 7 with triethylene glycol ac-
cording to a modified literature procedure (Figure 2).[19] Com-
Figure 3. Concentration-dependent zeta-potential (a) and DLS (b) measure-
ments of the bilayer coated nanoassemblies [TiO2-1]@4 in water. (*DLS of
pure [TiO2-1] in toluene). Uncertainty represents standard deviation of three
measurements.
tial smoothly increased from slightly negative values for pure
[TiO2-1] of z=À5 mV to z=À25 mV upon stepwise addition of
amphiphiles 4. The formation of the bilayer coated structure
led to the desirable electrosteric nanoparticle stabilization in
solution. A concentration of 0.5 mm was sufficient to stabilize
the 0.15 wt% nanoparticle dispersion in water.
In accordance with the zeta-potential measurements, DLS
measurements of the same particle dispersions revealed a de-
creasing average hydrodynamic particle size upon addition of
the stabilizing adlayer of 4 (Figure 3b). Although pure [TiO2-1]
rapidly formed large agglomerates in water, a dispersion of
[TiO2-1] in an aqueous solution of 4 (0.5 mm) resulted in
single-particle-stabilized colloidal dispersions, as characterized
by DLS. It is worth mentioning that, after centrifugation, the bi-
Figure 2. Synthetic procedures towards nonionic amphiphiles HC-PEG 4, FC-
PEG 5, and HC-FC 6.
pound 4 exhibits an alkyl moiety covalently linked to a glycol
moiety and, thus, represents a simple nonionic hydrocarbon– layer coated assemblies could be isolated as solids. The precip-
water surfactant. We also sought to investigate whether this
hydrophobic interaction driven self-assembly was transferrable
to other particle-capping ligands as well as other solvent envi-
ronments. Therefore, we synthesized amphiphiles HC-FC 5 and
FC-PEG 6, both consisting of a perfluorinated alkyl moiety co-
valently linked to either a hydrocarbon or a triethylene glycol
moiety (Figure 2). HC-FC 5 was synthesized through 1-ethyl-3-
(3-dimethylaminopropyl)carbodiimide (EDC) coupling of per-
fluorinated undecanoic acid 8 with dodecylamine yielding the
respective amide in 72% yield. An esterification of perfluorinat-
itates were re-dispersible in toluene (owing to the first-shell
coating) as well as in water (bilayer coated material), indicating
the adjustable surface energies through reversible formation of
the second-shell structures. The solid material was further char-
acterized by FTIR and TGA, which both supported the success-
ful formation of the molecular bilayer structure (see the Sup-
porting Information). The IR spectra of centrifuged and dried
bilayer coated particles displayed characteristic vibrational
bands of the phosphonic acids, which gave evidence that the
phosphonic acid ligands were indeed still bound to the metal
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oxide surfaces. In the TGA weight-loss curves of the bilayer
coated structures, the weight loss of 4 was observed in addi-
tion to the weight-loss step of covalently bound phosphonic
acid 1. The noncovalent nature of the second-shell binding fur-
ther resulted in desirable features such as reversibility (solubili-
ty in water and toluene) and exchangeability (exchange
against other amphiphilic molecules). Demonstration experi-
ments to prove that second-shell amphiphiles were easily ex-
changeable, but, once formed, assembled in close proximity to
the particle core, were conducted by employing fluorescent
marker amphiphiles 10 (Figure 4a).[25] Colored assemblies of
to an aqueous dispersion of [TiO2-3]. Similar to the self-assem-
bly of hydrocarbon-surfactant 4 with [TiO2-1], an increase of
particle dispersibility upon addition of 6 was immediately ob-
served. Figure 3a displays an image of the fluoroalkyl-function-
alized nanoparticles [TiO2-3] dispersed in pure water and a
0.5 mm aqueous solution of FC-PEG 6. Freshly prepared spray-
coated films of the nanoparticle assemblies demonstrated the
large variations of the static contact angles of water droplets
on these surfaces. Although spray-coated films of [TiO2-3] ex-
hibited superhydrophobic properties with a static contact
angle of water V>1608, a pre-treatment of these pristine
coated nanoparticles [TiO2-3] with amphiphiles 6 to form the
bilayer coated structures and a subsequent spray coating of
[TiO2-3]@6 revealed a static contact angle of water of V<208
(see images in Figure 3a). The hydrophobic-interaction-driven
self-assembly of the perfluorinated side chains of amphiphiles
6 with the fluorinated SAM of [TiO2-3] was further monitored
by DLS and zeta-potential measurements (see the Supporting
Information) as well as by UV/Vis spectroscopy (Figure 5b).
Figure 5. a) Images of [TiO2-3] in water before and after addition of stabiliz-
ing amphiphiles 6, and images of a water droplet on the surface of spray-
coated films of [TiO2-3] and [TiO2-3]@6. b) UV/Vis spectra of the particle dis-
persions in water and increase of the TiO2 band-gap absorption in the solu-
tions upon stepwise addition of amphiphiles 6, owing to enhanced colloidal
stability.
Figure 4. a) Structure of colored amphiphiles 10; b) a solution of 10 in water
and c) the same solution after addition of [Fe3O4-1] and sonication; d) the
solution becomes transparent upon magnetic extraction of the bilayer func-
tionalized nanoparticles to the sidewall of the glassware for 24 h; e) the
same solution upon addition of competing amphiphiles in excess, sonica-
tion, and magnetic removal of Fe3O4 nanoparticles from solution.
Here, we monitored the increasing band-gap absorption of the
TiO2 nanoparticles at l=320 nm of dispersions of [TiO2-3] in
water as a function of the added concentrations of 6. The
measurements supported our findings that concentrations of
>0.5 mm led to a full bilayer structure formation and, thus,
colloidal stability of [TiO2-3] in water. In another experiment,
we monitored the temperature-dependent zeta potential of
such nanoassemblies (Figure S5). It was found that the molecu-
lar bilayer self-assembled structure was stable over a wide tem-
perature range up to the boiling point of water.
functionalized titanium oxide particles [TiO2-PA-HC] with fluo-
rescent amphiphiles 10 became colorless upon centrifugation
and re-dispersion in a solution of competing amphiphiles (Fig-
ure S6). By using hydrophobically coated superparamagnetic
[Fe3O4-1] nanoparticles as scavengers, this mechanic extraction
could be extended towards a magnetic removal of amphi-
philes 10 from aqueous solution (Figure 4b–e). Interestingly,
upon re-dispersion and addition of competing amphiphiles in
excess, the second-shell ligands were replaced, leading to a re-
lease of 10 into water. This facile exchange of the second-shell
functionality gave further evidence of the reversibility of our
supramolecular binding concept.
The hydrophobic interaction-driven reversion of polarity
upon the addition of nonionic amphiphiles can also be readily
applied and generalized towards a solvophobic, in our case a
lipophobic and a fluorophobic, interaction-driven self-assem-
bly. Consistent with our previous experiments, a self-assembly
of fluorinated nanoparticles [TiO2-3] with hydrocarbon–fluoro-
carbon amphiphiles 5 led to an increase of the particle disper-
sibility when dispersed in a hydrocarbon solvent (toluene),
whereas addition of the same amphiphile 5 to a colloidal sus-
The pronounced stability of the bilayer coated structures en-
abled the fabrication of spray-coated films of the nanoparticle
assemblies on SiO2 wafers. The self-assembled structures were
sufficiently stable to demonstrate the variations of the surface
energies through static contact angle experiments. In one of
the most striking examples, we added nonionic amphiphiles 6
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pension of [TiO2-1] resulted in stable colloidal suspension in
perfluoromethylcyclohexane. Similarly, the solvent repellency
of [TiO2-2] when dispersed in lipophilic or fluorophilic media
decreased upon addition of amphiphiles 4 or 6, respectively. In
addition to monitoring the self-assembled structure formation
using DLS and UV/Vis techniques, measurements of the static
contact angles of three solvents (water, diiodomethane, and n-
hexadecane) on spray-coated films of these assemblies allowed
for the calculation of the surface energies of all mono- and bi-
layer coated nanoparticles. The results of these measurements,
which are displayed in Figure 6 (details in the Supporting Infor-
dynamic mechanism are general. We envision this coating con-
cept to facilitate technological processability of nanoparticles
and enable research on bilayer coated particulate assemblies
beyond the initial demonstrations described here such as a tar-
geted preparation of particulate carriers that selectively entrap
and release specific immiscible components.
Experimental Section
General Methods and Procedures
All reagents were purchased from commercial sources and used as
received, unless stated otherwise. Titanium oxide (anatase) nano-
particles with a specific surface area (SSA) of 46 m2 gÀ1 were pur-
chased from Nanograde (Stäfa, Switzerland) as a 20 wt% suspen-
sion in isopropanol. Iron oxide nanoparticles with an average parti-
cle diameter of 15 nm were purchased from Sigma–Aldrich as a
0.5 wt% suspension in water. The metal oxide nanoparticles were
functionalized in
a wet-chemical functionalization process in
0.15 wt% dispersions in isopropanol. To ensure full coverage, the
particles were exposed to 5.0 mm solutions of phosphonic acids
1–3.[19] The particles were functionalized in a volume of 25 mL, cor-
responding to approximately 30 mg nanoparticles. After adding
the phosphonic acid, the dispersions were sonicated for 30 min.
After functionalization, the mixture was centrifuged for 10 min
(14000 rpm). The functionalization included three washing steps. A
washing step included re-dispersion of the particles in isopropanol
followed up by another sonication step for 10 min and centrifuga-
tion. Finally, the particles were dried under vacuum or converted
into the desired solvent for characterization or follow-up experi-
ments, keeping the particle concentration constant (0.15 wt%). For
noncovalent functionalization of the pristine coated metal oxide
nanoparticles (second-shell coating), amphiphiles (4–6) were
added in varying concentrations to the pre-functionalized nanopar-
ticles [MOx-PA1-3] in 0.15 wt% dispersions in either water, isopro-
panol, perfluoro(methylcyclohexane), or toluene. Amphiphiles 4–6
were synthesized according to the detailed procedures described
below. The formation of homogenous dispersions in certain sol-
vents indicated a successful coupling. For analysis, such as zeta-po-
tential and DLS measurements as well as UV/Vis spectroscopy, the
suspensions were further diluted to obtain 0.015 wt% dispersions
of particles. To calculate the surface energies of the particle assem-
blies from the static contact angle, nanoparticle films were manual-
ly spray coated onto Si/SiO2 wafers with a 100 nm thermal oxide
layer. Before deposition of the films, the wafers were cleaned with
a 5 min oxygen plasma treatment at 200 W at a pressure of
0.2 mbar (Pico, Diener electronic GmbH, Germany). During the
spray-coating process, the substrate was heated to 1008C on a
hotplate. Static contact angles (SCA) were measured with a Data-
physics OCA 30 instrument (Data Physics Instruments GmbH, Ger-
many). SCA measurements were investigated by using the sessile
drop method, utilizing deionized water, diiodomethane, and n-hex-
adecane (1.0 mL) as probe liquids. More detailed information about
the experimental procedures and methods used is given in the
Supporting Information.
Figure 6. Surface energies of the mono- and bilayer coated nanoparticle as-
semblies (amphiphiles concentration in solution: 1.0 mm) calculated from
the average static contact angles of water, diiodomethane, and n-hexade-
cane on spray-coated thin films of the nanoparticle assemblies.
mation), show that the surface energies of pristine coated
nanoparticles [MOx-PA-HC], [MOx-PA-PEG], and [MOx-PA-FC]
were (statistically) significantly changed upon addition of non-
ionic amphiphiles 4–6. These findings gave final evidence that
the presence of simple nonionic amphiphilic molecules can
successfully decrease the interfacial tensions of stable precoat-
ed nanoparticles when dispersed in orthogonal solvents.
3. Conclusions
The combination of a strong covalent surface passivation and
a noncovalent, dynamic, and reversible self-assembly of amphi-
philes with pristine coated nanoparticles led to nanoparticles
that reversibly adjust their surface energies to certain solvent
environments, yielding colloidal stability that can be reversibly
alternated between hydrocarbons, water, and fluorocarbons. In
addition to this highly practical application of reversible nano-
particle dispersibility, this orthogonal tool kit for a switchable
nanoparticle functionalization was applied for 1) a selective
magnetic or mechanic scavenging of amphiphilic components
from solution and 2) preparation of particle thin films with
smoothly tunable wettability characteristics. The presented
method for the generation of bilayer coated particles and its
Synthesis
2-(2-(2-Hydroxyethoxy)ethoxy)ethyl dodecanoate (4) and fluores-
cent perylene bisimide amphiphiles 10 were synthesized according
to literature procedures.[26,27]
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N-Dodecyl-2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,11-henicosafluo-
roundecanamide (5): To an ice-cooled solution of perfluoro-n-unde-
canoic acid (282.05 mg, 0.5 mmol) in 20 mL dimethylformamide
and Processes” (GSAMP) and “Molecular Science” (GSMS) is grate-
fully acknowledged.
under
a
nitrogen
atmosphere,
4-dimethylaminopyridine
(122.17 mg, 1 mmol) was added. The resulting mixture was stirred
for 10 min at 08C, and then 1-HOBt (135.13 mg, 1 mmol) was
added. After stirring the mixture for 15 min, EDC (191.70 mg,
1 mmol) was added. Then, the mixture was stirred for 45 min at
08C. Finally, dodecylamin (278.04 mg, 1.5 mmol) was added and
the full reaction mixture was stirred for 3 days while the mixture
was warmed from 08C to room temperature. The solvent was re-
moved from the mixture under reduced pressure. The product was
purified by column chromatography [eluent: cyclohexane/tetrahy-
drofuran (THF), 1:1, Rf =0.5] to give 262 mg of a white crystalline
solid in 72% yield.
Conflict of Interest
The authors declare no conflict of interest.
Keywords: amphiphiles · colloidal stability · nanoparticles ·
surface energy · surfactants
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3
1H-NMR (400 MHz, [D8]THF): d=0.89 (t, 3H, J=7.2 Hz, CH3), 1.29–
1.32 (m, 18H, CH2), 1.55 (m, 2H, CH2), 3.29 (dt, 2H, 4J=6.8 Hz,
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3
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2-(2-(2-Hydroxyethoxy)ethoxy)ethyl-2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,
10,11,11,11-henicosafluoroundecanoate (6): Perfluoro-n-undecanoic
acid chloride was dissolved in 15 mL dichloromethane (DCM) and
5 mL THF. To the reaction mixture, triethylene glycol (TEG, 0.65 mL,
4.84 mmol) and triethylamine (0.3 mL, 2.12 mmol) were added. The
resultant solution was allowed to stir at room temperature over-
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luted with DCM and washed successively with water (2”10 mL)
and 0.5n HCl (10 mL ”2), and finally dried over magnesium sulfate.
The solvent was removed under reduced pressure and the crude
product was purified by column chromatography (eluent: EtOAC/
cyclohexane, 4:1, Rf =0.35) to give 6 in 85% yield.
1H-NMR (400 MHz, [D8]THF): d=2.75 (bs, 1H, OH), 3.45–3.48 (m,
2H, CH2), 3.53–3.62 (m, 6H, CH2), 3.71–3.78 (m, 2H, CH2), 4.52–4.55
(m, 2H, CH2) ppm. 13C-NMR (100 MHz, [D8]THF): d=62.1 (1C, ÀOÀ
CH2ÀCH2ÀOÀ), 67.9 (1C, ÀOÀCH2ÀCH2ÀOÀ), 68.6 (1C, ÀOÀCH2À
CH2ÀOÀ), 68.9 (2C, ÀOÀCH2ÀCH2ÀOÀ), 71.3 (1C, ÀOÀCH2ÀCH2ÀOÀ),
73.9 (1C, ÀOÀCH2ÀCH2ÀOÀ), 109.0 109.3, 111.4, 111.7, 116.6 (10C,
CF2), 158.5 (1C, C=O) ppm. 19F-NMR (376 MHz, [D8]THF): d=
À124.15 (m, 2F, CF2), À120.75 (m, 4F, CF2), À119.64 (m, 10F, CF2),
3
À116.82 (m, 2F, ÀCF2ÀCOOÀ), À79.16 (t, 3F, J=13.2 Hz, CF3) ppm.
FT-IR: n(OÀH) 3412; n(CH2) 2940, 2872; n(C=O) 1778; n(CÀF) 1202,
1146, 1072 cmÀ1. ESI-MS: m/z 697.04856 (M + H+), 714.07481(M +
NH4+). M.p.: 468C.
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Acknowledgements
Financial support from the Cluster of Excellence “Engineering of
Advanced Materials” (EAM), funded by the German Research
Council (DFG), and the Graduate Schools “Advanced Materials
Received: January 13, 2018
Version of record online March 5, 2018
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